1. Field of the Invention
The present invention relates to a layout designing/characteristic analyzing apparatus for designing a layout of a wiring board, and specifically to a layout designing/characteristic analyzing apparatus for a wiring board which analyzes the characteristics of a wiring board immediately after designing of a layout to obtain the results.
2. Description of Related Art
As the operation frequency of electronic circuits increases, causing the voltages to decrease for reduction in power consumption of the circuits, and as the packing density of the electronic circuits increases for miniaturization, measures against heat associated with the radiation and power consumption of electronic hardware are becoming important. Conventionally, it has been common to make prototype circuits to evaluate the effect of the measures. However, with the problems becoming increasingly difficult due to the above changes, there have been cases where many prototypes need to be repeatedly formed until an optimal solution is obtained. For this reason, an improvement in circuit developing techniques in terms of both development speed and cost has been desired.
Under such circumstances, a technique has been adopted which analyzes the radiation characteristics and heat distributions of a wiring board using a simulation tool to help solving the problems at the step before the preparation of a prototype wiring board There is known, for example, a layout designing/characteristic analyzing apparatus which includes a plurality of simulators such as a waveform simulator, timing simulator, heat simulator, EMC simulator and the like. This apparatus uses the analysis results obtained from these simulators for designing wiring boards (see, for example, Japanese Unexamined Patent Publication No. HEI 9(1997)-245076).
However, in EMC analysis, for example, a three-dimensional structure of a wiring board is formalized into a model and the current distributions in the board generated by circuit applied voltages are numerically expressed as integral equations so that their solutions can be determined using numerical integral calculus such as a moment method. Elemental currents that represent each of the obtained current distributions are superimposed to determine elemental currents inside the board. Then, based on each of the determined elemental currents, the electromagnetic field at each point is analyzed. According to the above-mentioned moment method, the integral equations are converted into linear equations and solved so that approximate solutions of the elemental currents representing the current distributions can be obtained. However, since the amount of calculation is enormous, it requires a great amount of time for computations. Heat analysis also takes a considerable amount of time for analysis, though not as much as the EMC analysis. For this reason, various analysis results can not immediately be obtained after the designing of a wiring board layout, and a layout designing/characteristic analyzing apparatus that can acquire the analysis results in a short time has been desired.
With respect to such a problem, there has been proposed means such as improvement in algorithm and adoption of a high-speed, large-size computer (see, for example, Japanese Unexamined Patent Publication No. HEI 10(1998)-319069). However, the former of the two means has not yet achieved an analysis time suitable for practical use and the latter has a problem in cost for achieving an analysis time suitable for practical use.
On the other hand, there has been known a technique of dividing a wiring board into modules to convert them into a library and using these modules which are compiled into the library to design interconnections on the wiring board (see, for example, Japanese Unexamined Patent Publication No. HEI 06(1994)-325126).
As the technology of designing by module formation advances as described above, the number of components on a wiring board increases while the time provided for the interconnection design is reduced. This complicates generation of an analysis model and analysis after layout designing of a wiring board, which makes an enormous amount of time to be taken for obtaining analysis results. Because of this, the difference widens between the time required for interconnection designing and the time required for analysis, meaning that most of the development period would be spent on the analysis if the current circumstances do not change.
There is also a method of simplifying models to reduce the time required for analysis. However, because the effect of simplification on analysis accuracy can not be simply estimated, the simplification of models not only requires time for preparing simplified models but also requires advanced knowledge.